1. Field of the Invention
The present invention relates to a developing device for use in an electrophotographic image forming apparatus and to an image forming apparatus incorporating the developing device. More particularly, the present invention relates to a trickle developing device that gradually supplies fresh developer and gradually discharge deteriorated developer and to an image forming apparatus incorporating the developing device.
2. Description of the Related Art
As developing systems employed for electrophotographic image forming apparatuses, the one-component developing system in which toner is used as the main component of the developer and the two-component developing system in which toner and carrier are used as the main components of the developer are known.
The two-component developing system that uses toner and carrier, in which the toner and carrier are charged by friction contact therebetween to predetermined polarities, has a characteristic that the stress on the toner is less than that in the one-component developing system that uses a one-component developer. Since the surface area of the carrier is larger than that of the toner, the carrier is less contaminated with the toner attached to the surface thereof. However, with the use for a long period, contamination (spent) attached to the surface of the carrier increases, whereby the capability of charging the toner is reduced gradually. As a result, problems of photographic fog and toner scattering occur. Although it is conceivable that the amount of the carrier stored in a two-component developing device is increased to extend the life of the developing device, this is undesirable because the developing device becomes larger in size.
To solve the problems encountered in the two-component developer, Patent document 1 discloses a trickle developing device being characterized in that fresh developer is gradually replenished into the developing device and developer deteriorated in charging capability is gradually discharged from the developing device, whereby the increase of the deteriorated carrier is suppressed. The developing device is configured to maintain the volume level of the developer inside the developing device approximately constant by discharging an excessive amount of deteriorated developer using the change in the volume of the developer. In the trickle developing device, the deteriorated carrier inside the developing device is gradually replaced with fresh carrier, and the charging performance of the carrier inside the developing device can be maintained approximately constant.
Furthermore, in a trickle developing device that uses a two-component developer, such a developing device as disclosed in Patent document 2 is proposed in which fluctuation of the discharge amount of the developer contained in a developer container due to tilting of the developer container is prevented.
In other words, the developing device according to Patent document 2 comprises a developer container equipped with a developer discharge port located at a position which is below the upper face level of the developer inside the developer container and in which the developer is always present; a developer discharge cylinder provided with a discharge port connecting section connected to a developer discharge port at one end thereof and a recovery container communicating section at the other end thereof; and a discharged developer conveying member for conveying the developer discharged from the developer discharge port and stored inside the developer discharge cylinder in a state of closing the discharge port connecting section toward the recovery container communicating section.    [Patent document 1] Japanese Patent Application Laid-Open Publication No. Sho 59-100471    [Patent document 2] Japanese Patent Application Laid-Open Publication No. Hei 11-065279
In the developing device disclosed in Patent document 2, the developer discharged into the developer discharge cylinder closes the discharge port connecting section to prevent further discharge of the developer, the discharged developer conveying member is driven to convey the developer closing the discharge port connecting section toward the recovery container communicating section located at the other end, and the developer newly delivered is discharged into the space emptied by the conveying. Furthermore, when the distribution of the amount of the developer inside the developer container becomes uneven due to the tilting or the like of the developer inside the developer container, the amount of the developer to be discharged from the developer container to the developer discharge cylinder is controlled by adjusting the rotation speed, the rotation operation time, etc. of the discharged developer conveying member.
In the developing device disclosed in Patent document 2, the amount of the developer to be discharged from the developer container to the developer discharge cylinder is controlled by adjusting the rotation speed, the rotation operation time, etc. of the discharged developer conveying member on the basis of the information on the tilting or the like of the developer inside the developer container. Hence, the developing device of Patent document 2 has problems such that some kind of detecting device is necessary to obtain the information on the tilting or the like of the developer inside the developer container and such that the control for the rotation speed, the rotation operation time, etc. of the discharged developer conveying member on the basis of the information obtained using the detecting device is complicated.
Accordingly, the technical problem to be solved by the present invention is to provide a developing device and an image forming apparatus capable of preventing the developer from being discharged excessively by using a simple configuration in the case that a trickle developing device that uses a two-component developer is in a tilted state.